The invention relates to internal combustion piston engines, in particular two-stroke opposed piston engines. A two-stroke opposed piston internal combustion engine comprises at least one cylinder, each cylinder being provided with a first piston and a second piston adapted to perform opposed motions in the cylinder,
each cylinder being provided with at least one intake port, a communication between an air intake arrangement and the cylinder via the intake port being dependent on the position of the first piston,
each cylinder further being provided with at least one exhaust port, a communication between an exhaust guiding arrangement and the cylinder via the exhaust port being dependent on the position of the second piston.
The invention also relates to a method of controlling a two-stroke opposed piston internal combustion engine, a method for controlling an internal combustion piston engine comprising a plurality of cylinders, a computer program and a computer readable medium for performing the steps of the methods, and a controller and an engine block for a two-stroke opposed piston internal combustion engine.
Here initially, some known characteristics and examples of a two-stroke opposed piston internal combustion engine as mentioned above are provided. The first and second pistons would normally be connected to at least one crankshaft. For example, as is known, the engine could present two crankshafts, and the first and second pistons could be connected to a respective of the crankshafts. Alternatively, as is also known, there could be one crankshaft, and one of the first and second pistons could be connected to the crankshaft by a linkage mechanism.
Further, as is known, the air intake arrangement could be presented by the engine to provide air to the cylinder. The air intake arrangement can comprise a single intake manifold, or more than one intake manifold, e.g. where the cylinders are arranged in a V-configuration. As is also known, the exhaust guiding arrangement could be presented by the engine to conduct exhaust gases from the cylinder. Similarly, the exhaust guiding arrangement can comprise a single exhaust manifold, or more than one exhaust manifold, e.g. where the cylinders are arranged in a V-configuration. Also, of course a fuel system could be provided for controlling the supply of fuel to the cylinders.
Herein, where reference is made to the communication between the air intake arrangement and the cylinder, the intention is to refer to a communication between an air intake arrangement and the interior space in the cylinder. Similarly, where reference is made to the communication between the exhaust guiding arrangement and the cylinder, the intention is to refer to a communication between the exhaust guiding arrangement and the interior space in the cylinder.
In order to keep emissions from a vehicle internal combustion piston engine as low as possible, it is of interest to keep the exhaust after treatment system (EATS) of such an engine operating efficiently during all modes of operation of the engine.
2-stroke opposed piston (2SOP) engines have a number of advantages over engines with one piston per cylinder. As a 2-stroke engine it has a higher power density than a 4-stroke engine, but provides also, compared to 2-stroke engines with one piston per cylinder, a more thorough purging of the cylinders since the intake and exhaust ports are provided at opposite ends of the cylinder liner.
2SOP engines have been the subjects of a number of proposals for improvements, for example for engine braking as described in US2012210985 A1. However, a problem with 2SOP engines that needs additional attention is that the exhaust temperature and exhaust pressure can be very low, and as a result from this the performance of an EATS can be poor. WO2013051968 describes, in a single piston per cylinder engine, cylinder deactivation at low load for increasing the exhaust temperature. Nevertheless, there is a need for providing further improvements of the EATS performance, in particular for 2 SOP engines.
It is desirable to improve the performance of an exhaust after treatment system (EATS) in an internal combustion piston engine, in particular a two-stroke opposed piston engine.
According to an aspect of the present invention, a two-stroke opposed piston internal combustion engine is provided comprising a plurality of cylinders, each cylinder being provided with a first piston and a second piston adapted to perform opposed motions in the cylinder,
each cylinder being provided with at least one intake port, a communication between an air intake arrangement and the cylinder via the intake port being dependent on the position of the first piston,
each cylinder further being provided with at least one exhaust port, a communication between an exhaust guiding arrangement and the cylinder via the exhaust port being dependent on the position of the second piston,
at least one of the cylinders being provided with an additional port and an additional port valve, a communication between the cylinder and an additional
conduit externally of the cylinder, via the additional port, being controllable with the additional port valve,
the air intake arrangement comprising at least one intake valve for selectively reducing or inhibiting air admittance to at least one of the cylinders with one intake valve per cylinder, or with a single intake valve being adapted to control air
admittance to more than one cylinder but less than all cylinders, wherein less than all cylinders are provided with additional ports, and the at least one intake valve is provided for selectively reducing or inhibiting air admittance to the remaining cylinders.
Herein, where reference is made to the communication between the additional conduit and the cylinder, the intention is to refer to a communication between the additional conduit and the interior space in the cylinder.
The exhaust temperature of 2SOP engines is particularly low at low engine loads, and is caused by the scavenge process this type of engine. If the EATS is located downstream of a turbo charger, the latter may cool the exhaust gases before reaching the EATS, and the result can be a very poor performance of the EATS. The invention is particularly beneficial where the engine is a diesel engine. As is known, in a two stroke diesel cycle the load is controlled with a fuel injector in each cylinder, whereas the amount of air admitted into the cylinder at each cycle is roughly the same at different loads. With the additional port and the additional port valve, it is possible to keep, during the compression stroke, after the intake and exhaust ports have been blocked by the pistons, the additional port valve open so that air can escape through the additional port, and close the additional port valve before the top dead centres are reached by the pistons and fuel is injected. Thereby, the additional port provides the function of an air removal port. This is particularly useful in low load operation in a diesel engine, since it will result in less air being trapped in the cylinder, giving a higher exhaust temperature. This in turn will improve the performance of the EATS during low loads.
Since the air intake arrangement comprises at least one intake valve for selectively reducing or inhibiting air admittance to at least one of the cylinders, during low loads the air supply to some cylinders can be terminated, while the additional port valves are activated in the remaining cylinders, providing a particularly effective manner of maintaining a high exhaust temperature. Thereby it is possibly to further increase the exhaust gas temperature and to further improve the performance of the EATS during low loads.
The intake valve arrangement can be provided such that there is one intake valve per cylinder.
Alternatively, a single intake valve can be adapted to control communication to more than one cylinder but less than all cylinders, i.e. a sub-group of the cylinders.
Less than all cylinders are provided with additional ports, and the at least one intake valve can be provided for selectively 1 educing or inhibiting air admittance to the remaining cylinders.
Such an arrangement would reduce the complexity and cost of the engine, since the additional port and the additional port valve is provided in only some of the cylinders.
During high loads it might be desired to utilize the entire air capacity of the cylinder and therefore to keep the additional port valve closed during the entire cycle. To provide for changing the operating mode of the additional port valve, a variable valve timing technology would be beneficial. Thereby it should be noted that the additional pmi valve can be actuated in a number of different ways, e.g. in a “cam less” manner, such as with a pneumatic valve technology, e.g. as in EP1299622, an electro-mechanical actuator, a hydraulic actuator, or a stepper motor, or using a cam shaft with cam switching, cam phasing, or an oscillating cam.
However, in some embodiments described below, the additional port valve remains open during the entire strokes of the respective cylinders, and thereby a simpler valve actuation can be used, and it could be e.g. hydraulic.
Preferably, the additional port is located such that, in an open position of the additional port valve, it allows communication between the cylinder and the additional conduit via the additional port when communication between the cylinder and the air intake arrangement via the intake port is blocked by the first piston, and communication between the cylinder and the exhaust guiding arrangement via the exhaust port is blocked by the second piston. Thereby, it is ensured that it is possible to keep, during the compression stroke, after the intake and exhaust ports have been blocked by the pistons, the additional port valve open so that air can escape through the additional port to reduce the amount of air trapped in the cylinder, to give a higher exhaust temperature.
Preferably, the intake port and the exhaust port are spaced apart in the longitudinal direction of the cylinder, and the additional port is located between the intake port and the exhaust port. This will also ensure that it is possible to keep the additional port valve open after the intake and exhaust ports have been blocked.
Preferably, the additional conduit is a part of, or is arranged to communicate with, the air intake arrangement. Thereby, it is ensured that air guided from the cylinder through the additional port will be kept in the “intake side” of the cylinder, and not contribute to cooling the exhaust gases.
Preferably, the additional port valve is a poppet valve. Thereby the additional port valve can be implemented in a fashion similar to inlet and exhaust valves in four stroke engines, which is well-established and readily available in the engine industry. However, alternatively, the additional port valve can be provided in some other manner, for example as a sliding sleeve as in US20081 15771 A1.
Preferably, the additional port valve is arranged so that a part of the additional port valve extends, in an open position of the additional port valve, into the cylinder, and the first and second pistons present respective recesses to accommodate said part of the additional port valve. Such recesses will provide for allowing the pistons to come close to each other as desired in a 2SOP engine, while providing for an effective additional port valve implementation, such as a poppet valve, extending into the cylinder in its open condition.
Preferably, the additional port is located such that top dead positions of the first and second pistons are symmetrically distributed with respect to the additional port. Thereby, the additional port can be centred in the longitudinal direction of the cylinder, providing an effective cylinder air removal function.
Preferably, where the additional port valve is arranged so that a part of the additional port valve extends, in an open position of the additional port valve, into the cylinder, the top dead centres of the first and second pistons are symmetrically located with respect to said part of the additional port valve. Thereby, where the pistons are provided with recesses as mentioned above, these recesses can be symmetric, which allows for the first and second pistons to be identical, which makes manufacturing easier and cheaper. Said part of the additional port valve can be symmetric with respect to a symmetry plane, the normal of the symmetry plane being parallel to the longitudinal direction of the cylinder, and the top dead centres can be symmetrically located with respect to said symmetry plane.
According to another aspect of the invention, a two-stroke opposed piston internal combustion engine is provided comprising at least one cylinder, each cylinder being provided with a first piston and a second piston adapted to perform opposed motions in the cylinder,
each cylinder being provided with at least one intake port, a communication between an air intake arrangement and the cylinder via the intake port being dependent on the position of the first piston, each cylinder further being provided with at least one exhaust port, a communication between an exhaust guiding arrangement and the cylinder via the exhaust port being dependent on the position of the second piston, at least one of the at least one cylinder being provided with an additional port and an additional port valve, a communication between the cylinder and an additional conduit externally of the cylinder, via the additional port, being controllable with the additional port valve, the additional port being offset from a symmetry plane, the normal of the symmetry plane being parallel to the longitudinal direction of the cylinder, and the top dead centres of the first and second pistons being symmetrically located with respect to the symmetry plane.
As understood, the additional port is offset from the symmetry plane in the longitudinal direction of the cylinder. Thereby the communication between the cylinder and the additional conduit externally of the cylinder via the additional port can be, in dependence of the offset direction, dependent on the position of the first piston or dependent on the position of the second piston. Thus, for activation of the exhaust temperature increasing operation, described above, in this aspect, the additional port valve can be opened and remain open throughout the cycles in the cylinder. Thereby a valve actuator for the additional valve can be provided in a simple and cost effective form. Where the additional conduit is connected to the air intake arrangement, the permanently open additional valve port might result in some exhaust gases entering the air intake arrangement; this might advantageously be used as an exhaust gas recirculation function.
It should be noted that this aspect can of course be combined with the aspect described above where the air intake arrangement comprises at least one intake valve for selectively reducing or inhibiting air admittance to at least one of the cylinders.
Preferably, a distance is provided between the additional port and the symmetry plane. Where the intake port and the exhaust port are located on opposite sides of the symmetry plane, the additional port can be located on the same side of the symmetry plane as the intake port. Thereby, the additional port can extend, in the longitudinal direction of the cylinder, closer to the symmetry plane than the intake port. Alternatively, the additional port can be located on the same side of the symmetry plane as the exhaust port, and the additional port can extend, in the longitudinal direction of the cylinder, closer to the symmetry plane than the exhaust port.
According to another aspect of the invention, a two-stroke opposed piston internal combustion engine is provided comprising at least one cylinder, each cylinder being provided with a first piston and a second piston adapted to perform opposed motions in the cylinder,
each cylinder being provided with at least one intake port, a communication between an air intake arrangement and the cylinder via the intake port being dependent on the position of the first piston, each cylinder further being provided with at least one exhaust port, a communication between an exhaust guiding arrangement and the cylinder via the exhaust port being dependent on the position of the second piston,                characterised in that at least one of the at least one cylinder is provided with an additional port and an additional port valve, a communication between the cylinder and the air intake arrangement via the additional port, being controllable exclusively with the additional port valve.        
As has been mentioned above, the additional port makes it possible the increase the exhaust temperature in a diesel engine. Since the communication between the cylinder and the air intake arrangement via the additional port is controllable exclusively with the additional port valve, it is ensured that air guided from the cylinder through the additional port will be kept in the “intake side” of the cylinder, and not contribute to cooling the exhaust gases. The communication between the cylinder and the air intake arrangement may be provided via an additional conduit externally of the cylinder. The additional conduit can be a part of, or be arranged to permanently communicate with, the air intake arrangement.
The additional port valve may be a poppet valve. The additional port valve may be arranged so that a part of the additional port valve extends, in an open position of the additional port valve, into the cylinder, and the first and second pistons present respective recesses to accommodate said part of the additional port valve.
According to another aspect of the invention, a method of controlling a two-stroke opposed piston internal combustion engine comprising at least one cylinder is provided, each cylinder being provided with a first piston and a second piston adapted to perform opposed motions in the cylinder,
each cylinder being provided with at least one intake port, and at least one exhaust port, at least one of the at least one cylinder being provided with an additional port and an additional port valve, a communication between the cylinder and an additional conduit externally of the cylinder, via the additional port, being controlled with the additional port valve,
the method comprising opening, in at least one of the at least one cylinder which is provided with an additional port and an additional port valve, the additional port between consecutive first and second top dead centre positions of the first piston, and subsequently, during a movement of the first piston towards the second top dead centre position, before the first piston has reached the second top dead centre position, closing the additional port after a transition from a condition with a communication between the air intake arrangement and the cylinder via the intake port, to a condition where the communication between the air intake arrangement and the cylinder via the intake port is blocked by the first piston.
Thereby, the additional port valve can be opened during introduction of air through the intake port, and closed after the intake port has been blocked by the first piston. This will allow some of the air introduced through the intake port to be expelled through the additional port during the compression stroke. Thereby the exhaust temperature can be kept high during low load engine operation.
To accomplish the steps of the method, the additional port may be opened and closed by opening and closing, respectively the additional port valve. Alternatively, for example where, as described above, additional port is offset from the symmetry plane between the piston top dead centres, the additional port may be opened and closed dependent on the position of the first or second piston.
Preferably, the step of opening the additional port is performed during a movement of the first piston away from the first top dead centre position, and after a transition from a condition where a communication between the air intake arrangement and the cylinder via the intake port is blocked by the first piston, to a condition with a communication between the air intake arrangement and the cylinder via the intake port. Thereby the additional port valve is not opened until the intake port is exposed to the interior cylinder space. Thus, the additional port valve is not opened during the expansion phase, and it is ensured that no exhaust gases are guided through the additional port.
Where the engine comprises a plurality of cylinders, and a fuel system for controlling the supply of fuel to the cylinders, the method can further comprise reducing or inhibiting the supply of air and fuel to a subgroup of the cylinders so as to inhibit combustion in the subgroup of the cylinders, the subgroup comprising at least one cylinder and less than all cylinders. Inhibiting combustion in the subgroup of the cylinders is advantageously performed simultaneously as the steps of opening and closing the additional port valves. In principle, the additional port valves in all cylinders can be opened and closed, as described above, while combustion in the subgroup of the cylinders is inhibited. However, alternatively, the additional port valves in the subgroup of cylinders in which the combustion is inhibited, can be kept closed, while the additional port valves in the remaining cylinders are opened and closed, as described above. Thereby, as also mentioned above, during low loads the air supply to some cylinders can be terminated, while the additional port valves are activated in the remaining cylinders, providing a particularly effective manner of maintaining a high exhaust temperature.
An aspect of the invention provides a method for controlling an internal combustion piston engine comprising a plurality of cylinders, a fuel system for controlling the supply of fuel to the cylinders, an air intake arrangement for controlling the supply of air to the cylinders, and an exhaust guiding arrangement to conduct exhaust gases from the cylinders, the method comprising                determining a value of an exhaust pressure related parameter, being the pressure of the exhaust gases in the exhaust guiding arrangement, or a correlated engine operation parameter, values of which are correlated to respective values of the pressure of the exhaust gases in the exhaust guiding arrangement,        comparing the determined value of the exhaust pressure related parameter to a predetermined threshold value of the exhaust pressure related parameter, —reducing or inhibiting, in dependence of the comparison between the determined value and the threshold value of the exhaust pressure related parameter, the supply of air and fuel to a subgroup of the cylinders, the subgroup comprising at least one cylinder and less than all cylinders, so as to inhibit combustion in the cylinder or cylinders in the subgroup.        
Inhibiting combustion in the cylinder(s) in the subgroup will deactivate the cylinder(s). This will provide an effective manner of reducing, during low load operation, the introduction of air through the engine. This is particularly beneficial in a 2SOP engine, especially where such an engine is provided as a diesel engine. During low load operation, deactivating and inhibiting air supply to the subgroup of cylinders will provide a higher pressure in the exhaust guiding arrangement which is beneficial to maintaining catalytic reactions in an exhaust after treatment system (EATS).
Preferably, where the engine comprises a turbo charger to pressurise air in the intake arrangement using energy of the exhaust gases in the exhaust guiding arrangement, the exhaust pressure related parameter is the pressure of the exhaust gases upstream of the turbo charger, or a correlated engine operation parameter, the values of which are correlated to the pressure of the exhaust gases upstream of the turbo charger. This embodiment is particularly beneficial where at least a part of the EATS is located upstream of the turbo charger, i.e. where a pan of, or the entire EATS is located upstream of turbo charger. As is known per se, the energy used by the turbo charger is provided by the pressure of the exhaust gases in the exhaust guiding arrangement upstream of the turbo charger. During low engine loads, this pressure falls. Where the turbo charger is a variable geometry turbo (VGT), a falling pressure in the exhaust guiding arrangement can to some extent be met with an adjustment of the turbo charger, as is known in the art. However, if the pressure falls below a certain level, the turbo charger will stop operating, reducing the pressure further, which can be disadvantageous for the operation of the EATS. By reducing or inhibiting at low loads, in dependence of pressure upstream of the turbo charger, the supply of air and fuel to the subgroup of the cylinders, it is possible to control and keep the exhaust pressure high enough for the turbo charger to keep operating. An operative turbo charger will further contribute to keeping the pressure in the air intake arrangement as well as the exhaust guiding arrangement relatively high, which again is beneficial to the processes in the EATS. The embodiment is particularly advantageous where the turbo charger is a variable geometry turbo (VGT) or a variable nozzle turbo (VNT).
The step of determining a value of the exhaust pressure related parameter can include detection of the exhaust pressure with a pressure sensor in the exhaust guiding arrangement. The pressure sensor is preferably located upstream of the turbo charger.
In some embodiments, the exhaust pressure related parameter is the pressure of the exhaust gases upstream of the EATS, or a correlated engine operation parameter, the values of which are correlated to the pressure of the exhaust gases upstream of the EATS. Where the exhaust pressure related parameter is the pressure, a pressure sensor located upstream of the EATS can be used. However, it is also possible for the exhaust pressure related parameter to be the pressure of the exhaust gases downstream of at least a part of the EATS and upstream of the turbo charger, or a correlated engine operation parameter, the values of which are correlated to the pressure of the exhaust gases downstream of at least a part of the EATS and upstream of the turbo charger.
Where a correlated engine operation parameter is used, such a parameter could be for example the engine load, values of which are correlated to respective values of the exhaust gas pressure upstream of the EATS. In some embodiments, the method can comprise providing
correlation data which correlates the values of the correlated engine operation parameter to the respective values of the exhaust pressure, and storing the correlation data in a data storage, wherein the step of determining a value of the exhaust pressure related parameter comprises determining a value of the correlated engine operation parameter.
Preferably, the correlation data is provided before operation of the engine. Preferably, the data storage in which the correlation data is stored is accessible to the controller.
Preferably, the engine comprises at least one intake valve for selectively blocking communication between at least one of the cylinders and the air intake arrangement, and the step of reducing or inhibiting the supply of air and fuel to a subgroup of the cylinders comprises selecting the subgroup of the cylinders, and controlling the intake valve so as to reduce or inhibit the supply of air to the subgroup of the cylinders. The intake valve(s) will thus provide the function of deactivating the cylinder(s) in the subgroup. Preferably, the engine is a two-stroke opposed piston internal combustion engine.
According to another aspect of the invention, a computer, a computer program, a computer readable medium are provided.
According to another aspect of the invention, a controller is provided for a two-stroke opposed piston internal combustion engine comprising at least one cylinder, each cylinder being provided with a first piston and a second piston adapted to perform opposed motions in the cylinder, each cylinder being provided with at least one intake port, and at least one exhaust port, at least one of the at least one cylinder being provided with an additional port and an additional port valve, a communication between the cylinder and an additional conduit externally of the cylinder, via the additional port, being controlled with the additional port valve, the controller being adapted to control a valve actuator so as for the additional port valve to assume a closed position and an open position, the open position allowing communication between the cylinder and the additional conduit via the additional port, the controller further being configured to perform the steps of a method according to an aspect of the invention.
Further, an engine block is provided for a two-stroke opposed piston internal combustion engine, presenting at least one cylinder, each cylinder being adapted to be provided with a first piston and a second piston adapted to perform opposed motions in the cylinder,                each cylinder being provided with, in a region to be swept by the first piston, at least one intake port for admittance of air into the cylinder,        each cylinder further being provided with, in a region to be swept by the second piston, at least one exhaust port for exit of gas from the cylinder,        
at least one of the at least one cylinder being provided with an additional port for providing a communication between the cylinder and an additional conduit externally of the cylinder, the additional conduit being presented by or connectable to the engine block,
the additional port being offset from a symmetry plane, the normal of the symmetry plane being parallel to the longitudinal direction of the cylinder, and the top dead centres of the first and second pistons being symmetrically located with respect to the symmetry plane.
As is known per se, the admittance of air through the intake port into the cylinder will depend on the position of the first piston. Also, exit of gas from the cylinder through exhaust port will depend on the position of the second piston. It is also understood that the intake port and the exhaust port are spaced apart in the longitudinal direction of the cylinder.
The benefits with the additional port, providing a communication between the cylinder and the additional conduit externally of the cylinder, have been explained above.